It appears that the 40% figure references this passage in the WWF/IUCN report:

“Up to 40% of the Brazilian forest is extremely sensitive to small reductions in the amount of rainfall. In the 1998 dry season, some 270,000 sq. km of forest became vulnerable to fire, due to completely depleted plant-available water stored in the upper five metres of soil. A further 360,000 sq. km of forest had only 250 mm of plant-available soil water left.”

Unfortunately I don’t have access to the full article but to call this reference “a complete load of porkies” seems a bit unjustified, unless it can be shown that Rowell and Moore completely misrepresent the Nature article (which of course *is* written by Amazonian specialists).

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The expression “a complete load of porkies” for what ended up in the IPCC AR4 WG-II Chapter 13, seems a bit justified indeed.

First of all it should not be up to the reader to dig down in the IPCC references until anything peer-reviewed is finally found. If Nepstad et al 1999 were the primary source for the “Up to 40%” claim, that article should have been used, stated and referenced as such, no matter what Rowell and Moore understood of it.

Secondly, the IPCC AR4 WG-II Chapter 13 makes no mention of Nepstad et al 1999. As far as I can see, the Nepstad et al 1999 article is only used in AR4 in the IPCC AR4 WG-II Chapter 4:

in some tropical and sub-tropical regions, notably South-East Asia and similarly the Amazon (e.g., Nepstad et al., 1999), deforestation rates are still high

You may note that in both cases Nepstad et al 1999 is used to mention deforestation (something one might expect out of an article titled Large-scale Impoverishment of Amazonian Forests by Logging and Fire).

Amazonian deforestation rates are used to determine human effects on the global carbon cycle and to measure Brazil’s progress in curbing forest impoverishment,,. But this widely used measure of tropical land use tells only part of the story..

Amazonian deforestation rates are used to determine human effects on the global carbon cycle(1-3) and to measure Brazil’s progress in curbing forest impoverishment(1,4,5). But this widely used measure of tropical land use tells only part of the story. Here we present field surveys of wood mills and forest burning across Brazilian Amazonia which show that logging crews severely damage 10,000 to 15,000 km(2) yr(-1) of forest that are not included in deforestation mapping programmes. Moreover, we find that surface fires burn additional large areas of standing forest, the destruction of which is normally not documented. Forest impoverishment due to such fires may increase dramatically when severe droughts provoke forest leaf-shedding and greater flammability; our regional water-balance model indicates that an estimated 270,000 km(2) of forest became vulnerable to fire in the 1998 dry season. Overall, we find that present estimates of annual deforestation for Brazilian Amazonia capture less than half of the forest area that is impoverished each year, and even less during; years of severe drought. Both logging and fire increase forest vulnerability to future burning(6,7) and release forest carbon stocks to the atmosphere, potentially doubling net carbon emissions from regional land-use during severe El Nino episodes. If this forest impoverishment is to be controlled, then logging activities need to be restricted or replaced with low-impact timber harvest techniques, and more effective strategies to prevent accidental forest fires need to be implemented.

It is hard not to notice that Nepstad et al 1999 were concerned about deforestation and fires possibly exarcebated by severe droughts, whilst Rowell and Moore, and the IPCC authors and reviewers, completely turned the cards around, pushing hard on the climatic side first.

The Brazilian jungle is surely not unique in becoming vulnerable to fire risk in dry season and drought, as forest always has been. But of course it is another useful recruit to be metamorphosed into another dire peril with bells on.

Congratulations Maurizio on digging this out, (it’s a dirty job, but someone’s got to do it) and congratulations to Delingpole for acknowledging your contribution. One of the minor wonders of this unfolding story is the way a lightweight gadfly journalist like Delingpole turns out to have a better understanding of scientific method than the President of the Royal Society.